1. Field of Invention
The present invention relates to methods and systems for treating cell proliferation disorders using derivatives of psoralen, that provide better distinction between normal, healthy cells and those cells suffering a cell proliferation disorder (hereafter “target cells”) and preferably that can be performed using non-invasive or minimally invasive techniques.
2. Discussion of the Background
Cell Proliferation Disorders
There are several types of cell proliferation disorders. Exemplary cell proliferation disorders may include, but are not limited to, cancer, bacterial infection, immune rejection response of organ transplant, solid tumors, viral infection, autoimmune disorders (such as arthritis, lupus, inflammatory bowel disease, Sjogrens syndrome, multiple sclerosis) or a combination thereof, as well as aplastic conditions wherein cell proliferation is low relative to healthy cells, such as aplastic anemia. Of these, cancer is perhaps the most well known. The term “cancer” generally refers to a diverse class of diseases that are commonly characterized by an abnormal proliferation of the diseased cells. A unifying thread in all known types of cancer is the acquisition of abnormalities in the genetic material of the cancer cell and its progeny. Once a cell becomes cancerous, it will proliferate without respect to normal limits, invading and destroying adjacent tissues, and may even spread to distant anatomic sites through a process called metastasis. These life-threatening, malignant properties of cancers differentiate them from benign tumors, which are self-limited in their growth and do not invade or metastasize.
The impact of cancer on society cannot be overstated. The disease may affect people at all ages, with a risk factor that significantly increases with a person's age. It has been one of the principal causes of death in developed countries and, as our population continues to age, it is expected to be an even greater threat to our society and economy. Therefore, finding cures and effective treatments for cancer has been, and remains, a priority within the biomedical research community.
Treatment Methods
Existing treatments for cell proliferation disorders such as cancer include surgery, chemotherapy, radiation therapy, immunotherapy, monoclonal antibody therapy, and several other lesser known methods. The choice of therapy usually depends on the location and severity of the disorder, the stage of the disease, as well as the patient's response to the treatment.
While some treatments may only seek to manage and alleviate symptoms of the disorder, the ultimate goal of any effective therapy is the complete removal or cure of all disordered cells without damage to the rest of the body. With cancer, although surgery may sometimes accomplish this goal, the propensity of cancer cells to invade adjacent tissue or to spread to distant sites by microscopic metastasis often limits the effectiveness of this option. Similarly, the effectiveness of current chemotherapy is often limited by toxicity to other tissues in the body. Radiation therapy suffers from similar shortcomings as other aforementioned treatment methods. Most of these cancer treatment methods, including radiation therapy, are known to cause damage to DNA, which if not repaired during a critical stage in mitosis, the splitting of the cell during cell proliferation, leads to a programmed cell death, i.e. apoptosis. Further, radiation tends to damage healthy cells, as well as malignant tumor cells.
A number of patents describe ex vivo treatment of bodily fluids, for example blood. Blood is obtained from a patient, treated with a photosensitive agent, exposed to UV radiation, and reinjected to the patient (i.e. extracorporeal photopheresis). Alternatively, a patient can be treated in vivo with a photosensitive agent followed by the withdrawal of a sample from the patient, treatment with UV radiation in vitro (ex vivo), and reinjecting the patient with the treated sample. This method is known for producing an autovaccine. A method of treating a patient with a photosensitive agent, exposing the patient to an energy source and generating an autovaccine effect wherein all steps are conducted in vivo has not been described. See WO 03/049801, U.S. Pat. No. 6,569,467; U.S. Pat. No. 6,204,058; U.S. Pat. No. 5,980,954; U.S. Pat. No. 6,669,965; U.S. Pat. No. 4,838,852; U.S. Pat. No. 7,045,124, and U.S. Pat. No. 6,849,058. Moreover, the side effects of extracorporeal photopheresis are well known and include nausea, vomiting, cutaneous erythema, hypersensitivity to sunlight, and secondary hematologic malignancy. Researchers are attempting to use photopheresis in experimental treatments for patients with cardiac, pulmonary and renal allograft rejection; autoimmune diseases, and ulcerative colitis.
A survey of known treatment methods reveals that these methods tend to face a primary difficulty of differentiating between normal cells and target cells when delivering treatment, often due to the production of singlet oxygen which is known to be non-selective in its attack of cells, as well as the need to perform the processes ex vivo, or through highly invasive procedures, such as surgical procedures in order to reach tissues more than a few centimeters deep within the subject.
U.S. Pat. No. 5,829,448 describes simultaneous two photon excitation of photo-agents using irradiation with low energy photons such as infrared or near infrared light (NRI). A single photon and simultaneous two photon excitation is compared for psoralen derivatives, wherein cells are treated with the photo agent and are irradiated with NRI or UV radiation. The patent suggests that treating with a low energy irradiation is advantageous because it is absorbed and scattered to a lesser extent than UV radiation. However, the use of NRI or UV radiation is known to penetrate tissue to only a depth of a few centimeters. Thus any treatment deep within the subject would necessarily require the use of ex vivo methods or highly invasive techniques to allow the irradiation source to reach the tissue of interest.
Chen et al., J. Nanosci. and Nanotech., 6:1159-1166 (2006); Kim et al., JACS, 129:2669-2675 (2007); U.S. 2002/0127224; and U.S. Pat. No. 4,979,935 each describe methods for treatment using various types of energy activation of agents within a subject. However, each suffers from the drawback that the treatment is dependent on the production of singlet oxygen to produce the desired effect on the tissue being treated, and is thus largely indiscriminate in affecting both healthy cells and the diseased tissue desired to be treated.
U.S. Pat. No. 6,908,591 discloses methods for sterilizing tissue with irradiation to reduce the level of one or more active biological contaminants or pathogens, such as viruses, bacteria, yeasts, molds, fungi, spores, prions or similar agents responsible, alone or in combination, for transmissible spongiform encephalopathies and/or single or multicellular parasites, such that the tissue may subsequently be used in transplantation to replace diseased and/or otherwise defective tissue in an animal. The method may include the use of a sensitizer such as psoralen, a psoralen-derivative or other photosensitizer in order to improve the effectiveness of the irradiation or to reduce the exposure necessary to sterilize the tissue. However, the method is not suitable for treating a patient and does not teach any mechanisms for stimulating the photosensitizers, indirectly.
U.S. Pat. No. 6,235,508 discloses antiviral applications for psoralens and other photoactivatable molecules. It teaches a method for inactivating viral and bacterial contaminants from a biological solution. The method includes mixing blood with a photosensitizer and a blocking agent and irradiating the mixture to stimulate the photosensitizer, inactivating substantially all of the contaminants in the blood, without destroying the red blood cells. The blocking agent prevents or reduces deleterious side reactions of the photosensitizer, which would occur if not in the presence of the blocking agent. The mode of action of the blocking agent is not predominantly in the quenching of any reactive oxygen species, according to the reference.
Also, U.S. Pat. No. 6,235,508 suggests that halogenated photosensitizers and blocking agents might be suitable for replacing 8-methoxypsoralen (8-MOP) in photophoresis and in treatment of certain proliferative cancers, especially solid localized tumors accessible via a fiber optic light device or superficial skin cancers. However, the reference fails to address any specific molecules for use in treating lymphomas or any other cancer. Instead, the reference suggests a process of photophoresis for antiviral treatments of raw blood and plasma.
U.S. Pat. No. 6,235,508 teaches away from 8-MOP and 4′-aminomethyl-4,5′,8-trimethylpsoralen (AMT) and many other photoactivatable molecules, which are taught to have certain disadvantages. Fluorescing photosensitizers are said to be preferred, but the reference does not teach how to select a system of fluorescent stimulation or photoactivation using fluorescent photosensitizers. Instead, the fluorescing photosensitizer is limited to the intercalator that is binding to the DNA. The reference suggests that fluorescence indicates that such an intercalator is less likely to stimulate oxygen radicals. Thus, the reference fails to disclose any mechanism of photoactivation of an intercalator other than by direct photoactivation by UV light, although use of a UV light probe or X-rays is suggested for penetrating deeper into tissues. No examples are provided for the use of a UV light probe or for use of X-rays. No example of any stimulation by X-ray radiation is taught.
Psoralens and Related Compounds
U.S. Pat. No. 6,235,508 further teaches that psoralens are naturally occurring compounds which have been used therapeutically for millennia in Asia and Africa. The action of psoralens and light has been used to treat vitiligo and psoriasis (PUVA therapy; Psoralen Ultra Violet A). Psoralen is capable of binding to nucleic acid double helices by intercalation between base pairs; adenine, guanine, cytosine and thymine (DNA) or uracil (RNA). Upon sequential absorption of two UV-A photons, psoralen in its excited state reacts with a thymine or uracil double bond and covalently attaches to both strands of a nucleic acid helix. The crosslinking reaction appears to be specific for a thymine (DNA) or a uracil (RNA) base. Binding proceeds only if psoralen is intercalated in a site containing thymine or uracil, but an initial photoadduct must absorb a second UVA photon to react with a second thymine or uracil on the opposing strand of the double helix in order to crosslink each of the two strands of the double helix, as shown below. This is a sequential absorption of two single photons as shown, as opposed to simultaneous absorption of two or more photons.

In addition, the reference teaches that 8-MOP is unsuitable for use as an antiviral, because it damages both cells and viruses. Lethal damage to a cell or virus occurs when the psoralen is intercalated into a nucleic acid duplex in sites containing two thymines (or uracils) on opposing strands but only when it sequentially absorbs 2 UVA photons and thymines (or uracils) are present. U.S. Pat. No. 4,748,120 of Wiesehan is an example of the use of certain substituted psoralens by a photochemical decontamination process for the treatment of blood or blood products.
Additives, such as antioxidants are sometimes used with psoralens, such as 8-MOP, AMT and I-IMT, to scavenge singlet oxygen and other highly reactive oxygen species formed during photoactivation of the psoralens. It is well known that UV activation creates such reactive oxygen species, which are capable of seriously damaging otherwise healthy cells. Much of the viral deactivation may be the result of these reactive oxygen species rather than any effect of photoactivation of psoralens. Regardless, it is believed that no auto vaccine effect has been observed.
The best known photoactivatable compounds are derivatives of psoralen or coumarin, which are nucleic acid intercalators. The use of psoralen and coumarin photosensitizers can give rise to alternative chemical pathways for dissipation of the excited state that are either not beneficial to the goal of viral inactivation, or that are actually detrimental to the process. For psoralens and coumarins, this chemical pathway is likely to lead to the formation of a variety of ring-opened species, such as shown below for coumarin:

Research in this field over-simplifies mechanisms involved in the photoactivating mechanism and formation of highly reactive oxygen species, such as singlet oxygen. Both may lead to inactivating damage of tumor cells, viruses and healthy cells. However, neither, alone or combined, lead to an auto vaccine effect. This requires an activation of the body's own immune system to identify a malignant cell or virus as threat and to create an immune response capable of lasting cytotoxic effects directed to that threat. It is believed, without being limiting in any way, that photoactivation and the resulting apoptosis of malignant cells that occurs in extracorporeal photophoresis causes the activation of an immune response with cytotoxic effects on untreated malignant cells. While the complexity of the immune response and cytotoxid effects is fully appreciated by researchers, a therapy that harnesses the system to successfully stimulate an auto vaccine effect against a targeted, malignant cell has been elusive, except for extracorporeal photophoresis for treating lymphoma.
Midden (W. R. Midden, Psoralen DNA photobiology, Vol I1 (ed. F. P. Gaspalloco) CRC press, pp. 1. (1988) has presented evidence that psoralens photoreact with unsaturated lipids and photoreact with molecular oxygen to produce active oxygen species such as superoxide and singlet oxygen that cause lethal damage to membranes. U.S. Pat. No. 6,235,508 teaches that 8-MOP and AMT are unacceptable photosensitizers, because each indiscriminately damages both cells and viruses. Studies of the effects of cationic side chains on furocoumarins as photosensitizers are reviewed in Psoralen DNA Photobiology, Vol. I, ed. F. Gaspano, CRC Press, Inc., Boca Raton, Fla., Chapter 2. U.S. Pat. No. 6,235,508 gleans the following from this review: most of the amino compounds had a much lower ability to both bind and form crosslinks to DNA compared to 8-MOP, suggesting that the primary amino functionality is the preferred ionic species for both photobinding and crosslinking.
U.S. Pat. No. 5,216,176 of Heindel discloses a large number of psoralens and coumarins that have some effectiveness as photoactivated inhibitors of epidermal growth factor. Halogens and amines are included among the vast functionalities that could be included in the psoralen/coumarin backbone. This reference is incorporated herein by reference.
U.S. Pat. No. 5,984,887 discloses using extracorporeal photophoresis with 8-MOP to treat blood infected with CMV. The treated cells as well as killed and/or attenuated virus, peptides, native subunits of the virus itself (which are released upon cell break-up and/or shed into the blood) and/or pathogenic noninfectious viruses are then used to generate an immune response against the virus, which was not present prior to the treatment.
Photodynamic Therapy (PDT)
Photodynamic therapy (PDT) is a treatment modality that uses a photosensitizing agent and laser light to kill cells. PDT retains several photosensitizers in tumors for a longer time than in normal tissues, thus offering potential improvement in treatment selectivity. See Corner C., “Determination of [3H]- and [14C] hematoporphyrin derivative distribution in malignant and normal tissue,” Cancer Res 1979, 3 9: 146-15 1; Young S W, et al., “Lutetium texaphyrin (PCI-0123) a near-infrared, water-soluble photosensitizer,” Photochem Photobiol 1996, 63:892-897; and Berenbaum M C, et al., “Meso-Tetra(hydroxyphenyl)porphyrins, a new class of potent tumor photosensitisers with favourable selectivity,” Br J Cancer 1986, 54:717-725. Photodynamic therapy uses light of a specific wavelength to activate the photosensitizing agent. Various light sources have been developed for PDT that include dye lasers and diode lasers. Light generated by lasers can be coupled to optical fibers that allow the light to be transmitted to the desired site. See Pass 1-11, “Photodynamic therapy in oncology: mechanisms and clinical use,” J Natl Cancer Inst 1993, 85:443-456. According to researchers, the cytotoxic effect of PDT is the result of photooxidation reactions, as disclosed in Foote C S, “Mechanisms of photooxygenation,” Proa Clin Biol Res 1984, 170:3-18. Light causes excitation of the photosensitizer, in the presence of oxygen, to produce various toxic species, such as singlet oxygen and hydroxyl radicals. It is not clear that direct damage to DNA is a major effect; therefore, this may indicate that photoactivation of DNA crosslinking is not stimulated efficiently.
Furthermore, when laser light is administered via external illumination of tissue surfaces, the treatment effect of PDT is confined to a few millimeters (i.e. superficial). The reason for this superficial limitation is mainly the limited penetration of the visible light used to activate the photosensitizer. Thus, PDT is used to treat the surfaces of critical organs, such as lungs or intra-abdominal organs, without damage to the underlying structures. However, even these treatments require significantly invasive techniques to treat the surface of the affected organs. Clinical situations use the procedure in conjunction with surgical debulking to destroy remnants of microscopic or minimal gross disease. It is possible that the laser light and small amount of remaining microscopic and minimal gross disease results in too little or highly damaged structures. Pre-clinical data show that some immune response is generated, but clinical trials have reported no auto vaccine effect similar to that produced by extracorporeal photophoresis in clinical conditions. Instead, immune response appears to be vigorous only under limited conditions and only for a limited duration.
Psoralen has been shown to have some activity against wild-type cancer lines in extracorporeal treatments, such as photodynamic therapy (PDT). However, many cancer lines are p53 mutant strains, which are more resistant to psoralen in treatments.
Problems
It is well recognized that a major problem associated with the existing methods of diagnosis and treatment of cell proliferation disorders is in differentiation of normal cells from target cells. Such target specificity is difficult to achieve by way of surgery since the strategy there is simply to cut out a large enough portion of the affected area to include all diseased cells and hope that no diseased cells have spread to other distant locations.
With chemotherapy, while some degree of differentiation can be achieved, healthy cells are generally adversely affected by chemo-agents. As in surgery, the treatment strategy in chemotherapy is also to kill off a large population of cells, with the understanding that there are far more normal cells than diseased cells so that the organism can recover from the chemical assault.
Radiation therapy works by irradiating cells with high levels of high energy radiation such as high energy photon, electron, or proton. These high energy beams ionize the atoms which make up a DNA chain, which in turn leads to cell death. Unlike surgery, radiation therapy does not require placing patients under anesthesia and has the ability to treat tumors deep inside the body with minimal invasion of the body. However, the high doses of radiation needed for such therapies damages healthy cells just as effectively as it does diseased cells. Thus, similar to surgery, differentiation between healthy and diseased cells in radiation therapy is only by way of location. There is no intrinsic means for a radiation beam to differentiate between a healthy cell from a diseased cell either.
Other methods may be more refined. For example, one form of advanced treatment for lymphoma known as extracorporeal photopheresis involves drawing the patient's blood from his body into an instrument where the white cells (buffy coat) are separated from the plasma and the red blood cells. A small amount of the plasma separated in this process is then isolated and mixed with a photosensitizer (PS), a drug that can be activated by light. The buffy coat is then exposed to a light to activate the drug. The treated blood is then returned to the patient. In this example, one may think of the target-specificity problem as being solved by separating the blood from the rest of the body where the target components are easily exposed.
However, this procedure has its drawbacks; it requires drawing blood from the patient, thus requiring cumbersome machinery to perform and may require blood transfusion in order to maintain the volume of blood flow in the machine. Further, this also limits the size of the patient that can be treated, since the extracorporeal volume is great and too much withdrawal of blood increases the risk of hypovolemic shock. The method is also limited to treating blood-born cell proliferation related disorders such as lymphoma, and is not capable of treating solid tumors or other types of non-blood related cell proliferation disorders.
A problem encountered in PDT therapy is the inability to treat target areas that are more than a few centimeters beneath the surface of the skin without significant invasive techniques, and the fact that PDT typically operates by generation of sufficient quantities of singlet oxygen to cause cell lysis. However, singlet oxygen in sufficient concentration will lyse not only target cells, but also healthy cells rather indiscriminately.
Therefore, there still exists a need for better and more effective treatments that can more precisely target the diseased cells without causing substantial side-effects or collateral damages to healthy tissues, and which are capable of treating even solid tumors or other types of non-blood related cell proliferation disorders. Additionally, while psoralen has been shown to have some activity against wild-type cancer lines in certain treatments, such as extracorporeal photopheresis and photodynamic therapy (PDT), many cancer lines are p53 mutant strains, which are more resistant to psoralen in treatments.
Accordingly, there is a need for derivatives of psoralen that can be used in such treatments for both wild-type and p53 mutant cancer cells.